The known way incremental position measurement systems normally increase the resolution specified by the period of a sampled grating pitch is by interpolating the resulting periodic signals. For this purpose, the periodic sampling signals are fed to downstream interpolation electronics, where the sampling frequency is multiplied and the measuring steps are thereby subdivided. A series of procedures and devices, with which further subdivision of the original measuring steps is possible, are known for analog interpolation. Digital interpolation procedures allow high signal subdivision up to a subdivision factor of several thousand.
A disadvantage of known incremental position measurement systems and their downstream interpolation electronics, as a rule, is that they have a fixed interpolation factor. Their interpolation electronics do not have the capability of making a targeted change in the interpolation factor once it has been set. Further, the interpolation factor cannot be varied during measurement operation itself.
However, German Patent Publication No. DD 288 221 and U.S. Pat. No. 4,630,928 suggest changing the interpolation factor as a function of the traversing speed of the parts moving relative to one another, in order to vary the factor as a function of speed between a coarse and a fine degree of resolution. This means that in the case of fast traversing speeds, a smaller interpolation factor would be used, while in the case of slower traversing speeds, higher interpolation factors can be selected. For this purpose, U.S. Pat. No. 4,630,928 proposes to make output signals or interpolation signals constantly available, which correspond to larger or smaller interpolation factors. Depending on the speed provided, one of the two signals is suppressed and the other output signal is always used for evaluation. The arrangement disclosed in German Patent Publication No. DD 288 211 processes the analog sampling signals according to the traversing speed through a higher-or lower grade counting module, so that either coarse or fine resolution output signals result.
Such arrangements to vary the interpolation factor are limited to switching between two discrete interpolation factors. However, it is desirable to provide several switchable interpolation factors, which can be alternately switched between during measurement operation. The two patent publications described do not disclose any information about this. In particular, the publications do not address how reliable signal processing can be ensured when switching between various interpolation factors during measurement operation.
Therefore, it is desirable to provide a method as well as a device to vary the interpolation factor in an incremental position measurement system during measurement operation. It is also desirable to provide several switchable interpolation factors and reliable signal processing so that position information is not lost during switching.